Electroplating with alkaline bath



Fatenteci Nov. 114, 1922.

UNHTED STATES i,l35,t37

PATENT OFFHQE.

CHARLES H. IPROCTOR, O18 ARLINGTON, AND CHETSTTAN JOHN WERNLUND, OJFWOOD- BRTDGE TOWNSHIP, IVZTDDLESEX COUNTY, NEW JERSEY, ASSIGNORS TO- THEROESS- TIER & HASSLACHER CHEMICAL COMPANY, A CORPORATION OF NEW YORK.

ELECTROPLATING WITH ALKALINE BATH.

lilo Drawing.

To all whom it may concern:

Be it known that we, CHARLns- HENRY 'Peoo'ron and CHRISTIAN JOHNWERNLUND, citizens. ofthe United States, and residents of Arlington,county of Hudson, State of New Jersey, and township of Woodbridge, inthe county of Middlesex and State of New Jersey, respectively, haveinvented certain new and useful Improvements in ElectroplatingwithAlkaline Bath, of which the following is a specification.

This invention relates to electroplating with zinc, and particularly toa process heretofore disclosed by us in an earlier application wherein asalt of mercury is added to an alkaline bath containing cyanide forraising the cathode potentialand thereby materially increasing thethrowing power of such baths as compared with baths previously known."The result of this is to obtain better coatings and also to enable castiron and irregular or recessed articles to be plated with zinc, whichhad heretofore been considered impracticable to be platedelectrolytically, or only with considerable difii culty.

The object of the present invention is to provide an improved method andapparatus and bath for introducing the mercury into the solution andmaintaining it there in substantially constant amount necessary toobtain the result vdesired, over a considerable period of time.

We have discovered that this object can be accomplished by incorporatingthe mercury in a predetermined percentage in the anode, constituting ineffect a mercury-zlnc alloy anode which is much superior either to anamalgamated zinc anode, or to the periodic replenishment of the mercuryin the bath by addition of soluble mercury salts.

By this invention, using a mercury-zinc alloy anode wherein the mercuryis predetermined of about one oer cent, we have found that the bath canbe operated without attention for upwards of a month and that thepercentage of mercury therein after a few hours run is substantially thesame at the endof a month or more. The practical advantage is that theoperator is not required to test the mercury content of the bath fromtime to time, nor to add mercury salts and yet the operating conditionsand the results remain practically constant Application filed December27, 1921. Serial No. 525,128.

throughout a long period. While our experiments have not determined theultimate operating period of such a bath automatically replenished fromthe anode, we have found that in runs of over a month the percentage ofmercury in solution is varied within less than 15% of that found in thebath after the initial run of a few hours necessary to bring it up toworking strength, and that such variation does not materially affect theresults.

For example, in one test extending over a period of over a month using azinc anode alloyed with 1% mercury, at the end of the initialeight-hours run the bath contained approximately 024% of mercury andafter over a months use contained approximately .021% variation inresults. In all cases, the throwing power of such a solution was foundto be Very materially increased over previous alkaline plating bathscontaining .cyantid without mercury, and the mercury was found to havethe effect of increasing the of mercury, without appreciable overvoltage of the cathode, the result of which is to decrease the amount ofhydrogen on the cathode.

In carrying out the invention, the article to be plated is first cleanedof both oxide, oil, grease, etc, by well understood methods includingsand blasting, weak acid or pickling, soda, etc, to expose a cleansurface, and is then immediately suspended from the cathode rod, or in acathode basket in the plating solution; The following bath gives goodresults:

Water 1 gal. Zinc cyanid 4oz. Sodium cyanide 4oz. Sodium hydroxid 202.

The anode consists of a pure form of zinc,

such as electrolytic alloyed with about 1% of mercury. We prefer to useone per cent, but this percentage can be increased or decreasedaccording to conditions.

Instead of bringing up the desired concentration of mercury in the bathby solu- ROB ' dried. The

The solution is maintained at a temperature of from 40 to 50 C. and thepreferred voltage is from three to six volts, depending upon thequantity of work being plated.

When the required deposit has been obtained, the article is removed,rinsed in cold and hot water successively, and then air tough and ofpleasing appearance and are more resistant to corrosion and abrasionthan any hitherto obtained in the art, and are found to contain a smallpercentage of mercury. 1

From tests made by us with and Without mercury in the bath (either fromthe anode or oz. of mercuric oxid added to the above bath) the effect ofthe mercury is to cause the voltage drop to increase, resulting infaster and greater deposition of metal coating and less decomposition ofelectrolyte and loss of hydrogen at the cathode. The effect is also notthat of a cathode depolarizer, but is to actually raise the cathodepotential up to such value that zinc is deposited rather than hydrogenreleased. In other words, there is an increased over voltage effect setup by the mercury at the cathode, which reduces hydrogen deposition andincreases the zinc and mercury deposition by the equivalentelectrochemical amount.

We do not limit ourselves to the particular proportions and percentagesherein specified, but the effect of too much mercury is to produce abrittle coating.

We do not claim broadly herein the addition of mercury to an alkalinezinc plating bath containing cyanid, as same is claimed broadly in aprior application filed by us December 3, 1921, Serial Number 519,7 65,but We do intend to claim broadly the incorporation of mercury into theanode for the purposes of the process herein described.

We are aware that it has heretofore been proposed to amalgamate zincanodes for acid zinc plating baths with mercury as Well as zincelectrodes for primary batteries, but are not aware that mercury hasbeen before known or used in a zinc anode to increase the over voltageof the cathode in an alkalin zinc plating bath containing cyanid, andtherefore do not restrict ourselves except as required by the scope ofthe appended claims.

The replenishment of mercury automaticall by solution from the anode asrequired, whi e maintaining a substantially constant amount of mercuryin solution, is especially deposits thus obtained are memes/5advantageous in practice because it obviates the necessity of makingchemical tests of the bath from time to time, as the operator simply hasto carry on the process. in the ordinary Way and gives no attention tothe mercury. The bath can be run for a number of weeks without attentionand with uniformity of result. Cast iron articles are plated as well assteel and Wrought iron are ticles, even in depressions andirregularities, whereassatisfactory results with cast iron in baths ofthis character have'heretofore only been obtained with difiiculty if atall.

What We claim is:

1. The method of zinc electroplating in a bath containing cyanide whichconsists in making the article to be plated the cathode, and providingan anode containing a substance which enters into the bath and increasesthe over voltage of the cathode.

2. The method of zinc electroplating in a bath containing cyanide whichconsists in making the article to be plated the cathode, and providingan anode containing such percentage of a substance which enters into thebath and increases the over voltage of the cathode while remaining insubstantially constant percentage in the bath.

3. The method of zinc electroplating in a bath containing cyanide whichconsists in making the article to be' plated the cathode,

and providing an anode containing a substance whichenters into the bathand increases the over voltage of the cathode while remaining insubstantially constant percentage in the bath.

4. The method of zinc electroplating in a bath containing cyanide whichconsists in making the artlcle to be plated the cathode, and providingan anode containing mercury.

5. The method of zinc electroplating in a bath containing cyanide whichconsists in making the article to be plated the cathode,

and providing an anode containing approximately 1% of mercury.

6. An anode for a cyanid zinc plating bath composed of zinc and a smallpercentage of mercury.

7. An anode for a cyanid zinc plating bath composed of zinc andapproximately 1% of mercury.

Signed atPerth Amboy, in the county of Middlesex and State of NewJersey, this 22d day of December A. D. 1921 CHARLES H. PROCTOR.CHRISTIAN JOHN WERNLUND.

